when hamlet realizes who the person being buried is, how does he react? is his reaction what you would expect based on his earlier actions?

Hamlet becomes shocked and saddened. He compares his love to Ophelia as being much stronger than that of Laertes,

I lov'd Ophelia; forty thousand brothers
Could not, with all their quantity of love,
Make up my sum"

This reaction sounds about right for Hamlet. He is prone to dramatic displays. Although he used Ophelia to his own ends, he still gives a good speech about what he has lost.